Likely Yamnaya incursion(s) into Northwestern Iran

Despite being stratigraphically dated to 5900-5500 BCE (ie. the Chalcolithic period), ancient sample Hajji_Firuz_ChL I2327 from Narasimhan et al. 2018, belongs to Y-haplogroup R1b-Z2103 and shows minor, but unambiguous, Yamnaya-related ancestry on the autosomes. Why is this a problem? Because both R1b-Z2103 and the Yamnaya culture are dated to the Bronze Age, and Yamnaya samples from Kalmykia and